The introduction of sulfate- and sulfur-containing waters into oil fields for secondary oil recovery often leads to formation of undesirable sulfur-containing compounds, particularly hydrogen sulfide, by sulfur-utilizing prokaryotes. These sulfur-containing compounds lead to safety, environmental, corrosion and plugging problems, and even premature abandonment of the oil and gas field.
Particularly, hydrogen sulfide generation begins by introducing sulfate- or other sulfur-containing aqueous solutions such as seawater into an anaerobic environment for indigenous microorganisms and microorganisms contained in the introduced aqueous solutions that are capable of producing hydrogen sulfide.
Hydrogen sulfide is a toxic, corrosive, flammable gas that causes problems in both the upstream and downstream oil and gas industry. Exposure to this gas, even at low concentrations, can cause serious injury or death. Hydrogen sulfide (H2S) in natural gas and crude oil reserves is often accompanied by small amounts of mercaptans (RSH), sulfides (R2S), polysulfides, and carbonyl sulfide (COS). Considerable expense and effort are expended annually to reduce the H2S content of gas and oil streams to make them suitable for commercial use.
Hydrogen sulfide has an offensive odor, and natural gas and crude oil streams containing substantial amounts of H2S are considered “sour.” In addition to natural gas and petroleum, there are also aqueous fluids that must be treated to reduce or remove H2S, such as waste water streams. Treatments to reduce or remove H2S from hydrocarbon or aqueous streams are referred to as “sweetening” treatments because the odor of the processed products is improved by the absence of hydrogen sulfide.
In some cases, nitrate introduction has been used to prevent sulfide formation in waters because specific nitrate-reducing bacteria (NRB) are activated and use volatile fatty acids (VFAs) and the carbon dioxide from dissolved limestone in the formation to produce nitrogen and/or ammonia. Thus, the NRBs could compete with the sulfur-utilizing prokaryotes and more rapidly use the VFAs, resulting in lowered production of sulfide and sulfur-containing compounds by the sulfur-utilizing prokaryotes.
However, this nitrate treatment can cause problems if the treatment is suspended or stopped because the hydrogen sulfide production would resume at the previous concentrations or the hydrogen sulfide production could even increase due to the enhanced biomass present. Additionally, some instances of nitrate application to reduce hydrogen sulfide have increased corrosion due to the incomplete reduction of the applied nitrate. The increased amount of NRB's can also lead to injectivity issues, where the microbial population blocks the injection path of the water into the reservoir.
Thus, a need exists for an effective and efficient method to prevent the generation of hydrogen sulfide and reduce the growth of or kill the microbes responsible for the production of hydrogen sulfide in a hydrocarbon-containing system comprising a water injection system, a hydrocarbon extraction system, or a hydrocarbon production system.